IMPACT OF URBANIZATION ON DECLINING GROUNDWATER LEVEL AND DRINKING WATER QUALITY IN GUWAHATI CITY, INDIA: TREND ANALYSIS AND HEALTH RISK ASSESSMENT

Urbanization alters hydrogeological conditions and causes stresses on the environment. The change in urban environment is largely driven by population growth, economic development, and modernization. The intensity of urbanization in recent decades is at an alarming level worldwide and it will likely follow the same trajectory in the future. Since the world’s population is growing rapidly, especially in urban areas, understanding how to sustainably meet increasing demand for water requires a detailed knowledge of the processes associated with long-term changes in water level and relevant groundwater quality. We analyzed temporal change in land use and land cover, water level and groundwater quality including trace elements and major ions in Guwahati that houses over one million people. The analysis of groundwater samples collected in February 2020 show As concentration ranges between 1.2 and 31 μg/l, which include 10 wells that show As >10 μg/l. Manganese concentration ranges between 21 and 4,100 μg/l, including 20 wells show Mn >400 μg/l. Fluoride concentration is between bdl (below detection limit) and 3.65 mg/l. The trend analysis shows water levels in some wells are decreasing while in other wells the water level remains steady or increasing. We show large-scale transformation of land for human use, which is further linked to decrease in the areas of high groundwater recharge zones. The decrease in groundwater recharge zones together with increase in drawdown to meet increasing demand for water has resulted in the decline in groundwater level. The cumulative effects of these have resulted in the change in aquifer geochemical processes that leads to release of contaminants in groundwater. Comparison of As and F concentrations in groundwater based on two-time measurements (2007 and 2020) show highly contaminated areas are mainly localized in the southeastern part of the study area. The spatial interpolation using IDW (inverse distance weighted) shows newer risk areas of high As (>10 μg/L) concentrations in groundwater during 2020. However, total risk areas remain unchanged. The high-risk prediction surface largely overlaps the areas where the land has been transformed for human use, such as building of new residential complexes and marketplaces. We estimated 160,000 people are likely consuming contaminated groundwater in 2020, as opposed to 110,000 people in 2007 based on a 1 km buffer region of high As and F wells. The results indicate an urgent need for sustainable urban planning to protect the quantity and quality of groundwater.